In a semiconductor device manufacturing process, an annealing process is performed to activate a dopant or the like. As for this annealing process, a microwave annealing process is proposed (e.g., Japanese Patent Application Publication No. 2009-516375). The microwave annealing process attracts attention as a next-generation annealing process, because it suppresses diffusion of impurities and allows formation of a thin activation layer. Further, it is reported that a loss of lattices can be recovered when the annealing is performed by microwaves.
A microwave generating unit is generally provided with a magnetron. When a wafer having a diameter of about 300 mm is used as an object to be annealed, a single magnetron cannot provide sufficient power and, thus, a plurality of magnetrons is required. However, when microwaves from a plurality of magnetrons are combined by irradiating them simultaneously, the electromagnetic waves (microwaves) from the magnetrons interfere with each other, contrary to the case of being combined in a plasma state, and the amount of reflection waves is increased. Accordingly, it is difficult to effectively supply a power.